This invention relates to a photoreceptor, particularly to a novel photoreceptor having a photosensitive layer containing an azo compound.
In the prior art, as electrophotographic receptors, there have widely been employed inorganic photoreceptors having photosensitive layers composed mainly of inorganic photoconductive compounds such as selenium, zinc oxide, cadmium sulfide, silicon, etc. However, these are not necessarily satisfactory in sensitivity, heat stability, humidity resistance, durability, etc. For example, selenium will be deteriorated in characteristics as the photoreceptor when crystallized and can be manufactured with difficulty, and also heat or fingerprint may cause crystallization to result in deterioration of performance as the photoreceptor. On the other hand, problems are involved in cadmium sulfide with respect to humidity resistance or durability, while zinc oxide poses problems in durability, etc.
In order to overcome the drawbackds possessed by inorganic photoreceptors, developments and researches have aggressively been made of organic photoreceptors having photosensitive layers composed mainly of various organic photoconductive compounds. For example, Japanese Patent Publication No. 10496/1975 discloses an organic photoreceptor having a photosensitive layer containing poly-N-vinylcarbazole and 2,4,7-trinitro-9-fluorenone. However, this photoreceptor is not necessarily satisfactory in sensitivity and durability. For improving such drawbacks, an organic photoreceptor with higher performance has been attempted to be developed by having the carrier generating function and the carrier transporting function assigned to different materials. Many studies have been made on such a photoreceptor of the so-called function separation type, since the respective materials can be selected from a wide scope of materials and photoreceptors having any desired performance can be prepared with relative ease.
In such a photoreceptor of the function separation type, a large number of compounds have been proposed. As an example employing an inorganic compound as the carrier generating material, Japanese Patent Publication No. 16198/1968 discloses an amorphous selenium, which can be employed in combination with an organic photoconductive compound. However, the carrier generating layer comprising the amorphous selenium is not improved in the drawback of being crystallized by heat to be deteriorated in charcteristics as the photoreceptor.
There have also been made many proposals about using organic dyes or organic dyes as the carrier generating material. For example, photoreceptors containing bisazo compounds or trisazo compounds in the photosensitive layer are already known as disclosed in Japanese Unexamined Patent Publication Nos. 22834/1979, 46558/1979, 46237/1981 and 196241/1982. However, these bisazo compounds or trisazo compounds are not necessarily satisfactory in characteristics of sensitivity, residual potential or stability during repeated uses, and also limited in scope of carrier transporting materials which can be selected, thus failing to satisfy sufficiently the wide range of requirements demanded by electrophotographic process.
Further, recourse has recently been made to gas lasers such as Ar laser, He-Ne laser, etc. or semiconductor lasers as the light source for photoreceptor. These lasers are characterized by capability of ON/OFF in time series, and expected to be promising as the light source for a copying having an image processing function, typically an intelligent copier as well as for a printer for output of a computer. Among them, semiconductor lasers are attracting attention, because they require no electrical signal/light signal transducing element such as acousatic optical element in nature, and also because they can be made to small scale and light weight. However, these semiconductor lasers are low in output as compared with gas lasers and the oscillated wavelength is longer (about 780 nm or longer), and therefore the photoreceptor of the prior art, of which spectral sensitivity is too much greater on the shorter wavelength side, can not be used as such as a photoreceptor using a semiconductor laser as the light source.
Moreover, an electrophotographic photosensitive member containing bisazo compounds in the photosensitive layer is already known as disclosed in Japanese Unexamined Patent Publication No. 194035/1983 (Our co-pending U.S. patent application Ser. No. 549,589). However, bisazo compounds used in a photoreceptor of the present invention are excellent in dispersibility and coating characteristics than the above application, and the photoreceptor of the present invention is excellent in electrified potential, durability and sensitivity than the above.